Wheat Disease Update – November 17, 2016
Dr. Kirk Broders, Plant Pathologist
Department of Bioagricultural Sciences and Pest Management
Colorado State University
The fall of 2016 has been significantly warmer on average in Colorado, with Denver hitting 80 degrees yesterday setting the daily record and tied the record for the month of November. This prolonged warm temperature and lack of precipitation has most of Colorado listed as being ‘abnormally dry’ or in ‘moderate drought’ according to the USDA Drought Monitor.
With this extended warm fall there is an increased chance for viral infection as the insects that vector these viruses are able to remain active for a long period and potentially infect more plants. In addition to viral symptoms you may also see early symptoms of stripe and leaf rust. I have received several reports of stripe rust and leaf rust from the Burlington and Holyoke areas. I have also received reports stripe and leaf rust from Nebraska and Oklahoma. This represents the second year in a row where stripe rust has been observed on fall-planted wheat in Colorado. This is likely attributed to 1) our extended above normal temperatures; 2) over-summering of the disease on volunteer wheat and/or grassy weeds which allows the fungus to remain in the area; and 3) spores being blown in from neighboring states where the rusts are still active. Fortunately, the dry weather is reducing the rate at which stripe rust spores can reproduce and spread, however the fluctuation in night and day temperatures allows dew to form on the leaves, allowing the fungus to infect, produce spores and spread.
Scout, but do not spray, for stripe and leaf rust in the fall. It is important to scout fields for rust in the fall, but do not apply fungicide in the fall. Instead, these fields should be noted and scouted early in the spring for the presence of active sporulation of stripe rust. If stripe rust appears on wheat in the fall, and there is consistent snow cover through the winter, the stripe rust pathogen has the ability to overwinter in Colorado, as was observed in a few locations in 2015-16. If there is active sporulation in the spring an early fungicide application is recommended to prevent further spread of the pathogen.
I am working with a graduate student to study the epidemiology of stripe rust in the central plains and develop predictive models for Colorado. If you have observed stripe rust or leaf rust in your fields, I encourage you to report these observations by responding to this email with information on the location and amount of disease present. We would like to visit these locations in the Spring to evaluate the potential of stripe rust to overwinter. I would also encourage you to send in samples of leaves infected with stripe rust if you come across any. Please contact me at 970-491-0850 if you are interested in participating in this study, and if you are willing to provide samples I can provide you with a protocol.
Kirk D. Broders, PhD Assistant Professor Department of Bioagricultural Sciences and Pest Management Colorado State University firstname.lastname@example.org